The invention relates to a device for applying a ventrally or dorsally directed translatory force onto a lower leg in the area of a knee joint for treatment or follow-up treatment of knee instability, in particular cruciate ligament instability.
In the field of knee instability, posterior cruciate ligament lesions in particular pose considerable medical problems. Although there are well proven surgical reconstruction procedures for posterior cruciate ligament ruptures and other lesions of the posterior cruciate ligaments, the result of surgery has often deteriorated after a few months, or been lost altogether, because the sutured or reconstructed ligament has been stretched again in an undesired manner on account of the gravitational force of the lower leg which, with the patient lying on his back, acts in the dorsal direction. This leads to incorrect positioning of the tibia relative to the femur, as is indicated by broken lines in FIG. 1. By contrast, the solid lines in FIG. 1 show the tibia and the lower leg in the normal state. The risk of this kind of incorrect positioning, i.e. dropping of the tibia relative to the femur, also arises of course when a posterior cruciate ligament lesion is treated, not surgically, but by conservative methods.
In the case of anterior cruciate ligament instability, a problem which may occur is that the tibia comes to lie too far in the ventral direction relative to the femur. This is especially the case when the articular surface of the patient's tibia is inclined in such a way that, in the upright position in which the femur presses on the oblique articular surface of the tibia, a force is exerted in the ventral direction on the tibia. If the anterior cruciate ligament is unstable, the tibia in the area of the knee joint is displaced forward in an undesired manner, i.e. upward as shown in FIG. 1.
A device is already known for applying a ventrally or dorsally directed translatory force onto the lower leg in the area of the knee joint, which device is intended to counteract this undesired shifting of the tibia. This known device has thigh bars which are arranged medially and laterally in the area of the thigh and which can be secured on the thigh by means of a cuff. A swivel lever is mounted in an articulated manner at the distal end of the thigh bars which are located laterally alongside the knee, which swivel lever is pretensioned either in the ventral direction or in the dorsal direction by means of a spring. This swivel lever engages under or over a bolt protruding laterally from a lower-leg cuff in an area of the lower leg close to the knee. Depending on how the pretensioning of the spring is directed, the upper end of the tibia is urged either in the ventral direction or the dorsal direction in order to counteract an undesired stretching of a damaged posterior or anterior cruciate ligament and an associated translatory displacement of the tibia in the dorsal or ventral direction. A problem with this known device, however, is that the spring force on the lower leg means that a permanent force is exerted in the extension direction or flexion direction, i.e. a torque which seeks to permanently extend or flex the lower leg. A free and unimpeded extension or flexion of the knee is therefore not possible with this known device.